The following is the cumulative frequency distribution (of less than type) of $1000$ persons each of age $20$ years and above. Determine the mean age.

Age below (in years)	$30$	$40$	$50$	$60$	$70$	$80$
Number of persons	$100$	$220$	$350$	$750$	$950$	$1000$

If the means of the following frequency distribution is $18$, find the missing frequency.

If the sum of the frequencies is $120$ and the mean is $50$ then find the sum of missing frequencies.

The daily income of a sample of $50$ employees are tabulated as follows:

Find the mean daily income of employees. 

The following is the distribution of height of students of a certain dass in a certain city:

Find the median height.

Following is the distribution of I.Q. of $100$ students. Find the median I.Q.

If the median salary of the following data giving salaries of $280$ persons is $₹\mathrm{S}$, then find the value of $\mathrm{S}$ (to the nearest whole number).

Calculate the median from the following data: